The present invention relates to a disposable safety syringe comprising:
a) a syringe barrel;
b) an injection needle, being integral with a needle-carrier, which is fitted on the tapered fore end of the syringe barrel;
c) a plunger which is slidable in the syringe barrel and has an injection stroke which extends from a retracted syringe-filling position to an advanced syringe-emptying position, and is fitted at its back with a manually drivable stem, driven out of the syringe barrel through the open rear end thereof;
d) a needle-covering sleeve, which is axially fitted on the syringe barrel, so as to slide from a retracted rest position, in which it leaves the needle exposed, into an advanced safety position, in which it entirely covers the needle;
e) hook-like interacting means, which are provided at the rear side of the syringe barrel and at the rear side of the needle-covering sleeve, and are initially engaged with each other so as to retain the needle-covering sleeve in its retracted rest position, whereas they are automatically disengaged from each other by the plunger stem, in the last portion of the injection stroke of the plunger, thereby releasing the needle-covering sleeve;
f) a spring, interposed between a spring-bearing projection on the rear end of the syringe barrel and a spring-bearing projection, inside the needle-covering sleeve, which stresses the needle-covering sleeve, once it is released from the hook-like means, towards its advanced safety position, first by making it elastically adhere to the patient body, and then by progressively advancing it, on extracting the needle from the patient body, at the end of the injection, until it entirely covers the extracted needle;
g) clamping means which automatically lock the needle-covering sleeve in its advanced safety position, preventing it from axially moving in either direction;
h) the means for locking the needle-covering sleeve in its advanced safety position are held and/or formed at least partially by a mounted sleeve-clamping ring, which is provided and preferably mounted and fitted on the fore end of the syringe barrel.
i) one or more retaining tongues, preferably formed of one piece with the sleeve-clamping ring and extending forwards in the axial direction by their free fore ends, which retaining tongues may be elastically moved radially inwards, that is towards the longitudinal axis of the syringe;
k) one or more retaining teeth provided on the inner part of the needle-covering sleeve, each associated to a tongue for retaining the sleeve-clamping ring, each of these retaining teeth being provided with a rear flank which is substantially transverse to the longitudinal axis of the syringe and interacts as a bearing surface with the free end of the retaining tongue associated thereto, and with a fore flank, which is inclined forwardly radially outwards and interacts as a deflecting surface with the free end of the retaining tongue associated thereto;
l) a radial stop projection, which is provided at the rear end of the sleeve-clamping ring and interacts as an abutment with an inner stop projection of the needle-covering sleeve;
m) all this in such a way that, in the last portion of the forward stroke of the needle-covering sleeve, the retaining tooth/teeth thereof elastically and radially push, by their inclined fore flanks, the associated retaining tongue/s inwards, passing beyond them, and enabling them to elastically snap radially outwards, so as to engage their free fore ends with the transverse rear flanks of the associated retaining tooth/teeth, while the inner stop projection of the needle-covering sleeve contacts the rear abutment projection of the sleeve-clamping ring.
A disposable safety syringe of this kind is known from the documents U.S. Pat. No. 5,562,626, WO-A-93/00949 and EP-A-0 467 173. In the disposable safety syringes known from these documents, the needle-covering sleeve has an all around circular inner section profile and an all around circular smooth outer section profile, and the retaining teeth which cooperate with the retaining tongues of the sleeve-clamping ring protrude inwardly from said circular inner section profile of the needle-covering sleeve, thus determining a corresponding outer diameter of said sleeve.
With respect to these known syringes, the disposable safety syringe according to the invention is characterized in that the retaining tongues of the sleeve-clamping ring are slidably engaged by their free fore ends in corresponding inner longitudinal grooves of the needle-covering sleeve, in which grooves their respective retaining teeth are provided, and said inner longitudinal grooves of the needle-covering sleeve are formed in corresponding outer longitudinal ribs of the needle-covering sleeve.